Not destroying the Pirates first thing can work to your advantage. Most factions will not have the fleets to fight for trade spots with them and if you build up before moving to the trade theaters or taking out the Pirates you will likely have better trade spots.
Ttpically I blockade the pirates ports to prevent them building many ships until I have a big enough force to deal with them,then once I've finished them,move into the trade zones with enough ships to try to grab all the zones at once.